Rollers for conveyor belts are arranged so that the conveyor belt travels thereover in a downstream belt travel direction and path. However, conveyor belts can tend to meander or mistrack laterally toward one side or the other of the rollers due to reasons such as uneven loads carried by the belt. Conveyor belt tracking devices have been developed that respond to belt mistracking to attempt to redirect the belt back to its correct travel path substantially centered on the conveyor rollers.
One type of belt tracking device configured to correct a misaligned belt has sensor rollers that are mounted to arms that are each operatively connected to a frame for tracking or training rollers under a belt. If the belt becomes misaligned, it will forcefully engage the sensor roller at the misaligned side, which will cause the arms to force the belt training roller to pivot for steering the belt back toward its proper downstream travel path. However, the sensor rollers are generally located upstream or downstream of the training rollers to create the necessary moment arm for pivoting the rollers. This upstream or downstream mounting of the sensor rollers means that the correcting mechanism is limited to use when the belt travels in a single direction. Furthermore, this solution requires the edge of the belt to forcefully make contact with the sensor rollers, which can undesirably damage the belt.
One type of belt tracker that avoids the use of sensor rollers is disclosed in U.S. Pat. No. 6,405,854 to Cumberlege. The Cumberlege system includes a pair of rollers mounted to an elongate support shaft that is pivotable about its center relative to a support frame. The shaft includes a vertical post that pivots within a cylindrical bushing mounted to the support frame. The rollers include an outwardly decreasing taper at the outer ends, which operate to cause the rollers mounted to the elongate shaft to pivot in a horizontal plane about the vertical axis to steer a misaligned belt back toward its proper downstream travel path. The rollers can be mounted to the shaft either in a trough configuration or in a non-troughed or flat configuration. In the troughed configuration, the rollers pivot about the vertical axis while maintaining their orientation relative to the vertical pivot axis. This configuration is limited, however, because the disclosed system is not capable of tilting or raising an outer end of the roller to provide additional steering control over a mistracking belt.
Another belt tracking device that avoids the use of sensor rollers has an inclined pivot axis of the rollers located upstream of the rollers. This belt tracker is disclosed in U.S. Pat. No. 2,225,276 to Parker and includes an idler roller that is pivotal about a pivot axis that is upwardly inclined in the downstream direction. In this regard, when a conveyor belt mistracks toward one end portion of the idler roller, the drag forces acting downstream on the idler roller end portion increase, urging the end portion to shift downstream, while the downstream tilt of the pivot axis causes the idler roller end portion to also simultaneously shift downwardly under the increased weight of the mistracked belt passing over the end portion. Thus Parker's belt tracker utilizes the weight of the conveyor belt and drag forces acting on the end portion toward which the belt is mistracking to energize the idler roller to pivot about the pivot axis. However, the Parker belt tracker is limited because the tilt of the pivot axis restricts its use to belts that travel in a single direction.
A belt tracking apparatus is disclosed in U.S. Patent Application Publication No. 2011/0272250 assigned to the Applicant herein. The belt tracking apparatus has an inclined pivot axis. However, the pivot axis is located downstream of the idler tracking roller so that when the tracking roller pivots about the included pivot axis, the one end portion of the roller that shifts downstream will also simultaneously shift upwardly for urging the mistracking belt back toward its correct travel path. The belt tracking apparatus of the '250 publication also relies on engagement between an edge of the belt and the corresponding one of the sensor rollers to generate the energizing force for pivoting the tracking roller so that its end portion is shifted downstream and upwardly. Further, because the tracking roller pivots about an inclined pivot axis, shifting of the roller end portion upwardly will be dictated by the angle of the inclination of the pivot axis and the amount of downstream shifting of the roller end portion. In other words, the inclination of the pivot axis defines a predefined relationship between the amount of downstream shifting of the tracking roller end portion and the amount of upward shifting thereof when the tracking roller is pivoted for correcting a mistracking conveyor belt. This can require that greater energizing force be generated from the sensor roller for actuating the pivoting of the tracking roller since it simultaneously has its end portion shifted both downstream and upwardly. In addition, the use of sensor rollers and an inclined pivot axis restricts use of the '250 publication tracking apparatus to conveyor belts that travel in a single direction.
Another known belt tracking apparatus is disclosed in U.S. Patent Application Publication No. 2013/0284565 assigned to the Applicant herein. The disclosed apparatus includes a support frame for mounting the apparatus to the conveyor belt system, a tilt channel device mounted to the support frame so that the tilt channel device can shift laterally and tilt relative to the support frame, and a roller assembly mounted to the tilt channel device so as to be rotatable and pivotable. Accordingly, the frame assembly is configured to allow the reaction force from the conveyor belt caused by the downstream shifting of an end portion of an idler roller due to mistracking of the conveyor belt for directing or steering the belt back toward its correct travel path to be used for energizing a tilting action of the idler roller to raise the downstream end portion thereof.